The ACLU and its Wisconsin chapter sent complaints to the U.S. Department of Education's civil rights office in Chicago alleging that Riverview Middle School in Barron and Robinson Elementary School and McLenegan Elementary School in Beloit were violating Title IX, a federal law banning sex discrimination in education.

ACLU officials alleged that Riverview separated its fifth-grade math and language arts classes by sex in 2011. The school discontinued the program this year but plans to reinstate next year. Robinson Elementary has been offering single-sex programs in multiple subjects since 2007, while McLenegan Elementary began offering single-sex classes in the fourth and fifth grades in the 2011-12 school year.

The complaints said neither school district has offered adequate justification for separating boys and girls, relying on discredited scientific theories about how girls and boys learn differently.

"We all want children in Wisconsin to have a quality education, but tracking them into programs that promote stereotypes doesn't help anyone," Karyn Rotker, a civil liberties attorney with ACLU Wisconsin, said in a statement. "Whatever the intentions of the educators who set up these programs, the disproven theories on which they rely actually limit opportunities for boys and girls alike."

Melissa Badger, community relations coordinator for the Beloit School District, disputed the ACLU's assertions. She said the curriculum is the same for single-sex classes and combined-sex classes at the two elementary schools and parents can choose which classes their children attend.

Messages left after-hours Thursday afternoon at the Barron school district's offices and at the U.S. Department of Education's civil rights office weren't immediately returned.

An estimated 500 public schools across the country offer some single-sex classes. Proponents argue the separation allows for more tailored instruction and reduces gender-related distractions such as flirting. Critics contend the movement promotes harmful gender stereotypes and deprives students of equal educational opportunities.